It is known that mono-1-olefins (α-olefins), including ethylene, can be polymerized with catalyst compositions employing titanium, zirconium, vanadium, chromium or other metals, impregnated on a variety of support materials, often in the presence of cocatalysts. These catalyst compositions may be useful for both homopolymerization of ethylene, as well as copolymerization of ethylene with comonomers such as propylene, 1-butene, 1-hexene, or other higher α-olefins. Therefore, there exists a constant search to develop new olefin polymerization catalysts, catalyst activation processes, and methods of making and using catalysts, that will provide enhanced catalytic activities and polymeric materials tailored to specific end uses.
One type of catalyst system comprises organometal compounds, particularly metallocene compounds. Often, metallocene compounds are used in catalyst compositions along with activating cocatalysts such as aluminoxanes or organoboron compounds. Therefore, it is of interest to develop metallocene-based catalytic systems that can be activated with different, possibly less-expensive activating agents, yet still provide good polymerization activities. It is also of interest to develop metallocene-based catalytic systems that polymerize olefins without the need for cocatalysts.